The last few years have witnessed a growing number of large-scale installations of wireless, local area networks (WLANs). Although these large-scale WLANs can deliver packetized data via Internet connectivity and the like to individual users, efficient mechanisms for delivering data to groups of users is still lacking. Such mechanisms are critical to the distribution of live broadcasts as well as stored multi-media streams, radio channels and TV channels (i.e., multicasting).
Though it may appear at first glance that broadcast and multicast services can be easily supported by existing WLANs because each access point (AP) in a WLAN may send broadcast messages to all of its associated users, there exists a shortage of non-interfering frequencies in large-scale WLANs.
For instance, the widely-used 802.11 b/g standards only support three non-interfering frequencies. This means that adjacent APs in a WLAN often use the same transmission frequency. As a result, transmissions from such APs often interfere with one another. This significantly degrades the quality of any service that relies upon broadcast and multicast transmissions.
One possible solution is to send the message, etc., that is intended to be broadcast to each user individually (so-called “unicast” transmissions). However, such a solution does not exploit the broadcast capability of a wireless network and generates significant overhead.
It is desirable, therefore, to provide multicast-based methods and devices for large-scale WLANs that avoids or minimizes interference and avoids the need to generate a significant amount of overhead required.
It is further desirable to address two other challenges associated with large-scale WLANs. First, it is desirable to optimize the time allocated to APs (e.g., the shorter the better) when transmitting multicast packets in order to reduce the impact on unicast services. Second, it is desirable to properly schedule transmissions from neighboring stations, either APs or users, in order to minimize the amount of multicast packets that are lost due to interference.